Method for operating a belt retractor and a belt retractor for a safety belt

ABSTRACT

In a method for operating a belt retractor, the belt retractor comprising a belt tensioner drive and with a pre-tensioner drive which can both exert a torque onto a belt spool in a direction for winding a safety belt, the pre-tensioner drive is prevented from exerting a torque onto the belt spool through the activation of the belt tensioner drive. In a belt retractor for a safety belt, having a belt spool, a pre-tensioner drive with a drive motor, which can turn the belt spool in the winding direction for the purpose of pre-tensioning the safety belt, and with a belt tensioner drive which can drive the belt spool for the purpose of a belt tensioning, a safety mechanism is provided, which through an activation of the belt tensioner drive prevents the pre-tensioner drive from driving the belt spool in the winding direction.

The invention relates to a method for operating a belt retractor.

BACKGROUND OF THE INVENTION

The invention in particular relates to a belt retractor which is provided with a belt tensioner drive and with a pre-tensioner drive, which can both exert a torque onto a belt spool in a direction for winding the safety belt. The invention additionally relates to a belt retractor for a safety belt, with a belt spool, a pre-tensioner drive with a drive motor which can rotate the belt spool for the purpose of pre-tensioning the safety belt in the winding direction, and with a belt tensioner drive which can drive the belt spool for the purpose of a belt tensioning.

Both the pre-tensioner drive and also the belt tensioner drive basically serve to drive the belt spool in the winding direction when a vehicle state exists which is classified as critical, so that the so-called belt slack of the safety belt is eliminated and the safety belt lies taut against the body of a vehicle occupant who is to be restrained. The pre-tensioner drive differs from the belt tensioner drive firstly in that the pre-tensioner drive operates reversibly. When, after the pre-tensioning of the safety belt, the vehicle situation which was classified as critical is no longer present, the belt spool is returned into its initial position in the unwinding direction, so that the tension in the safety belt drops again. A belt tensioner drive, on the other hand, can only act on the belt spool in one direction, namely turn it in the winding direction. A returning is basically not possible. Generally, it is also not possible because the belt tensioner drive is only triggered in those situations which subsequently require the exchange at least of the belt retractor together with the belt tensioner drive. Secondly, the pre-tensioner drive differs from the belt tensioner drive with regard to the forces applied onto the safety belt. The pre-tensioner drive applies traction forces in the order of magnitude of 100 N onto the safety belt. These forces, when they occur during the travel operation, are generally not felt to be unpleasant by the vehicle occupant. A belt tensioner drive, on the other hand, tensions a safety belt with a much higher force (distinctly above 1000 N); when the safety belt lies with this force against the body of the vehicle occupant, this would be felt to be unpleasant in the normal travel state. Owing to the differences mentioned with regard to the mode of operation of the pre-tensioner drive on the one hand and the belt tensioner drive on the other hand, also structural differences result. A pre-tensioner drive generally has an electric motor as drive element. A belt tensioner drive, on the other hand, usually operates with a pyrotechnic gas generator and a piston which converts the generated gas pressure into a movement.

In addition to the pre-tensioner drive and the belt tensioner drive, modern belt retractors have a force limiter system by which the forces are limited which are present at a maximum in the safety belt and therefore also act on the body of the vehicle occupant. Usually, the force limiter systems make it possible that despite the blocking of the belt spool, a particular length of the safety belt can be withdrawn from the belt retractor against a high, defined force. The force-limiter systems are coordinated here with the airbag systems, likewise used in the vehicle, in order to exert as uniform a restraining effect as possible together with a gas bag unfolding in front of the vehicle occupant.

If, after the tensioning of the safety belt, the force-limiting system responds, i.e. for example in the case of a vehicle accident, it cannot be reliably predetermined whether the pre-tensioner drive has been activated previously or is still active. If the pre-tensioner drive is still coupled with the belt spool, this leads to the traction force in the safety belt, which is necessary for withdrawal of the safety belt from the belt retractor, not only resulting from the resistance provided by the force-limiter system, but also from the resistance which is necessary to rotate the pre-tensioner drive in the unwinding direction of the safety belt, i.e. in a direction contrary to the current direction of action of the pre-tensioner drive. In other words, higher forces occur in the safety belt when the pre-tensioner drive is active than is actually provided (on the basis of the design of the force-limiter system).

The object of the invention consists in providing a method for operating a belt retractor, and also a belt retractor, in which the force which is necessary with a belt spool which is blocked per se for withdrawal of the safety belt and which is defined by the force limiter system, is not altered by the respective operating state of the pre-tensioner drive.

BRIEF DESCRIPTION OF THE INVENTION

In order to solve this problem, the invention provides a method in which, when the belt tensioner drive is activated, through the activation of the belt tensioner drive the pre-tensioner drive is prevented from exerting a torque on the belt spool. A belt retractor according to the invention is distinguished in that a safety mechanism is provided, which with an activation of the belt tensioner drive prevents the pre-tensioner drive from driving the belt spool in the winding direction. In this way, it is ensured that the force level provided by the force-limiter system is not “falsified” by the pre-tensioner drive; irrespective of whether the pre-tensioner drive has been activated or not, the pre-tensioner drive does not have to be carried along in the unwinding direction of the safety belt, when after activation of the belt tensioner drive a high force is acting in the safety belt, which leads to the response of the force-limiter system.

According to a preferred embodiment of the invention, through the activation of the belt tensioner drive the flux of force from the pre-tensioner drive to the belt spool is interrupted. In this way, the belt spool can turn freely from the pre-tensioner drive in the unwinding direction when the force-limiter system responds. The pre-tensioner drive does not need to be carried along.

According to a further preferred embodiment of the invention, provision is made that the pre-tensioner drive has an electric motor and that through the activation of the belt tensioner drive the current supply of the electric motor is interrupted. This prevents the electric motor from acting on the belt spool in the winding direction if the belt spool were to in fact rotate in the opposite direction under the action of the force effective in the safety belt, i.e. in the unwinding direction, in order to realize a force-limiting function. Then only the electric motor has to be carried along; the torque occurring here is, however, comparatively small, so that the force defined by the force-limiter system in the safety belt is not substantially increased.

According to a further embodiment of the invention, provision is made that the pre-tensioner drive has an electric motor and that through the activation of the belt tensioner drive, the electric motor is operated in a direction for unwinding of the safety belt. In this state, the electric motor therefore assists the unwinding of the safety belt from the belt spool and hence the response of the force-limiter system. As the torque provided by the electric motor is comparatively small, a negligible effect is produced on the force level provided by the force-limiter system, from which the force-limiting function is realized.

According to the invention, provision is made that the belt tensioner drive has a pyrotechnic gas generator which through its activation prevents the pre-tensioner drive from exerting a torque on the belt spool. This has the advantage that no external additional control is necessary in order to uncouple the pre-tensioner drive from the belt spool or to reverse its direction of rotation; the uncoupling or reversal of the direction of rotation of the pre-tensioner drive can be achieved with the gas pressure which is provided by the belt tensioner drive for the purpose of the belt tensioning.

Advantageous embodiments of the invention will be apparent from the sub-claims.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is described below with the aid of preferred embodiments which are illustrated in the enclosed drawings. In these:

FIG. 1 shows a diagrammatic view of a belt retractor according to the invention with pre-tensioner drive and belt tensioner drive;

FIG. 2 shows a diagrammatic view of a safety mechanism used in the belt retractor of FIG. 1 in the initial state;

FIG. 3 shows the safety mechanism of FIG. 2 in the activated state;

FIG. 4 shows a diagrammatic section through a belt retractor according to a second embodiment of the invention;

FIG. 5 shows a diagrammatic section through a belt retractor according to a third embodiment of the invention;

FIG. 6 shows diagrammatically a cut-out of the pre-tensioner drive of a belt retractor according to a fourth embodiment of the invention in the initial state;

FIG. 7 shows the cut-out of FIG. 6 with activated safety mechanism;

FIG. 8 shows diagrammatically a part of the pre-tensioner drive of a belt retractor according to a fifth embodiment of the invention, the safety mechanism being situated in its initial position;

FIG. 9 shows diagrammatically the cut-out of FIG. 8, the safety mechanism having been activated;

FIG. 10 shows diagrammatically a cut-out of a pre-tensioner drive of a belt retractor according to a sixth embodiment of the invention, the safety mechanism being situated in its initial state;

FIG. 11 shows the cut-out of FIG. 10, the safety mechanism having been activated;

FIG. 12 shows diagrammatically a switching diagram for a belt retractor according to a seventh embodiment of the invention;

FIG. 13 shows diagrammatically a switching diagram of a belt retractor according to an eighth embodiment of the invention, the safety mechanism being in its initial position; and

FIG. 14 shows the switching diagram of FIG. 13, the safety mechanism being in its activated state.

DETAILED DESCRIPTION OF THE INVENTION

In FIG. 1, a belt retractor 10 is shown diagrammatically, which has a frame 12 and a belt spool 14 mounted in the frame 12. A safety belt 16 is held on the belt spool 14. A blocking system 18 is provided, indicated diagrammatically, with which the belt spool can be blocked in a belt band—sensitive and/or vehicle-sensitive way. In addition, a spring cassette 20 is provided, which surrounds a winding spring (not shown), which exerts a torque onto the belt spool 14 in a direction which leads to the winding of the safety belt 16. In addition, a force-limiter system 22 is provided, which is illustrated here as a torsion rod 22 arranged inside the belt spool 14. The precise construction and mode of operation of the blocking system 18 and of the force limiter system 22 are of no importance for the invention, so they are not explained further here.

The belt retractor 10 is provided with a belt tensioner drive 24 which has a pyrotechnic gas generator 26. The latter can generate a gas, which is under pressure, on activation, which acts on a piston (not illustrated), which in turn drives the belt spool 14 in the winding direction of the safety belt 16. In addition, a pre-tensioner drive 28 is provided, which has an electric motor 30 as drive motor. This can be coupled via a gear and/or a coupling with the belt spool 14 so that it can drive the latter both in the winding direction and also in the unwinding direction of the safety belt 16.

The pre-tensioner drive 28 has a safety mechanism 32, which is formed here by a separating element 34 and an actor 36. The actor 36 is formed here as a piston/cylinder drive, the cylinder beam being coupled with the pyrotechnic gas generator 26 and the piston being coupled with the separating element 34. The separating element 34 is arranged so that it can engage on a belt drive 38 between the electric motor 30 and the belt spool 14.

In the initial position (see FIG. 2), the belt drive 38 is intact. The electric motor 30 can therefore drive the belt spool 14 in the winding direction and in the unwinding direction of the safety belt 16. When the belt tensioner drive is activated, i.e. the pyrotechnic gas generator 26 is ignited, the latter firstly drives the belt spool 14 in the winding direction of the safety belt 16. At the same time, a portion of the generated compressed gas is branched off for the safety mechanism 32, so that the actor 36 moves the separating element 34 from the initial position shown in FIG. 2 into a separating position shown in FIG. 3. In this, the separating element 34 has destroyed the belt drive 38 mechanically, in particular has cut the belt of the belt drive, so that a mechanical connection no longer exists between the electric motor 30 and the belt spool 14. If then, after completion of the belt tensioning, such a force is acting in the safety belt 16 that the force limiting system 22 responds and the belt spool 14 is turned by the safety belt 16 in the unwinding direction, this takes place entirely without impairment by the pre-tensioner drive 28, because a mechanical connection no longer exists between the electric motor 30 of the pre-tensioner drive 28 and the belt spool 14.

In FIG. 4 a second embodiment is shown. The safety mechanism 32 also has an actor 36 here, which can move a separating element 34. In the same manner as in the embodiment according to FIGS. 2 and 3, the separating element is constructed as a sharp blade. This blade acts here on a shaft 40 which connects the pre-tensioner drive 28 with the belt spool 14. Through activation of the pyrotechnic gas generator 26, the actor 36 moves the separating element 34 in the direction of the arrow P, whereby the shaft 40 is separated, sheared off or otherwise broken. Provision can be made that the shaft 40 is provided with a nominal fracture site.

In FIG. 5 a third embodiment is shown. Instead of the shaft 40, here a connecting pin 42 leads between the pre-tensioner drive 28 (symbolized here by a pinion) and the belt tensioner drive 24 (symbolized here by a pinion coupled with the belt spool 14). The connecting pin can be transferred by the actor 36 (formed here by a pressure chamber which is closed of from one end side of the connecting pin 42 and can be acted upon by the pressure of the compressed gas generated by the gas generator 26) in the direction of the arrow from the initial position shown in FIG. 5, in which the pre-tensioner drive 28 is coupled with the belt spool 14, into a separating position in which the connecting pin 42 no longer engages into the pinion of the belt tensioner drive 24 and thereby the connection to the belt spool 14 is interrupted.

In FIGS. 6 and 7 a fourth embodiment is shown. Here, also, a connecting pin 42 is used, which can be transferred from an initial position (see FIG. 6) into a separating position (see FIG. 7). In the initial position, the connecting pin 42 connects two toothed wheels 50, 52 which are part of a gear 54 between the electric motor 30 of the pre-tensioner drive and the belt spool 14. In the initial state, the connecting pin 42 provides a torque-transferring connection between the two toothed wheels 50, 52. At the same time, it serves for mounting. A slider 56 engages on the connecting pin 42, which slider can be acted upon by the actor 36 so that it draws the connecting pin 7 in the direction of the arrow P into the separating position. In the latter, the torque-transferring connection between the two toothed wheels 50, 52 is interrupted, so that the belt spool can turn in the unwinding direction without the electric motor 30 having to be entrained.

According to a further development of the invention, provision can be made that the safety mechanism 32 acts on a coupling 60 which is provided between the electric motor 30 of the pre-tensioner drive and the belt spool 14. This coupling is indicated diagrammatically in FIG. 6. The safety mechanism 32 can be constructed so that it prevents a transfer of force via the coupling. For this purpose, for example the catches of the coupling can be brought out of engagement and be blocked so that a renewed guiding in is not possible. It is also possible to uncouple the region of the force transfer catches from the rest of the housing. Finally, the teeth on the axis into which the force transfer catches engage can be closed or covered, so that a torque transfer is not possible and the catches slip through.

In FIGS. 8 and 9 a fifth embodiment is shown. Here, also, a gear 54 is used between the electric motor 30 of the pre-tensioner drive and the belt spool 14. The gear 54 is constructed as a planetary gearing, in which the sun wheel is coupled with the drive motor and the hollow wheel is coupled with the belt spool. The planetary wheels are mounted in a diagrammatically illustrated planetary wheel carrier 70 which is supported so as to be fixed to the frame. The safety mechanism here has a separating element 34 again, which can be moved by an actor from the initial position shown in FIG. 8 into the separating position shown in FIG. 9, in which the support of the planetary wheel carrier 70 on the frame 12 of the belt retractor is interrupted. In this way, a torque transfer via the gear 54 is no longer possible, so that the force-limiting function can act unimpaired by the pre-tensioner drive.

In FIGS. 10 and 11, a sixth embodiment is shown. Here, also, a gear 54 is used between the electric motor 30 of the pre-tensioner drive and the belt spool 14. The gear 54 is constructed here as a worm gear. The worm shaft is supported at one end via a support element 80 on the frame 12. The actor 36 can transfer the support element 80 from the initial position shown in FIG. 10 into the separating position shown in FIG. 11, in which the end of the worm shaft associated with the support element 80 is freed. If a torque is to be transferred between the electric motor 30 and the belt spool 14, this can be deflected upwards in the direction of the arrow P so that a torque transmission is prevented.

According to a further development (not illustrated) of the invention, provision can be made that after the pyrotechnic tensioning by the belt tensioner drive 24, both the belt tensioner drive 24 and also the pre-tensioner drive 28 are uncoupled from the belt spool 14 by the reverse rotation of the belt spool 14 being used for the uncoupling. For this purpose, for example catches of the couplings, which are used to couple the pre-tensioner drive 28 and the belt tensioner drive 24 with the belt spool 14, can be brought out of engagement through an axial displacement.

In FIG. 12 a seventh embodiment is shown. In this, the ignition current for the pyrotechnic gas generator 26 controls an electronic circuit or a relay in the control apparatus for the reversible tension unit, i.e. for the pre-tensioner drive 28, which exchanges the polarity of the supply voltage of the electric motor 30. Thereby, the electric motor 30 attempts to drive the belt spool 14 in the unwinding direction, whereby the coupling used to couple the electric motor 30 with the belt spool 14 opens, so that the electric motor is uncoupled from the belt spool 14.

In FIGS. 13 and 14, an eighth embodiment of the invention is shown. In this embodiment also the polarity of the supply lines of the electric motor 30 is exchanged through the ignition current of the pyrotechnic gas generator 26. This takes place here through a switch 90 which is activated by the ignition current of the gas generator and switches a switch unit 92 from the initial state shown in FIG. 13 into the state shown in FIG. 14 with reversed polarity.

According to a further development of the invention, not illustrated, provision can be made that through ignition of the pyrotechnic gas generator 26, at least one supply line of the electric motor 30 is interrupted. This can be realized for example through actuation of a switch which is either actuated by the ignition current for the pyrotechnic gas generator 26 or by the compressed gas generated thereby. It is also possible to lay at least one supply line of the electric motor 30 so that on ignition of the pyrotechnic gas generator 26 it is separated through the action of the pressure thus generated. Thereby, the electric motor 30 together with the gear can be turned backwards with little effort of force. In addition, it is possible to lay at least one supply line of the electric motor 30 so that it is separated mechanically by a belt buckle or an end fitting when this is moved by a belt buckle tensioner or an end fitting tensioner. Finally, it is possible to mechanically short-circuit the two supply lines of the electric motor 30 through the activation of the pyrotechnic gas generator 26, so that the securing of the current supply of the electric motor is activated, whereupon the latter becomes currentless. 

1. A method for operating a belt retractor, said belt retractor being provided with a belt tensioner drive and with a pre-tensioner drive, both said belt tensioner drive and said pre-tensioner drive being adapted to exert a torque onto a belt spool in a direction for winding a safety belt, the method containing the following steps: activating said belt tensioner drive, preventing said pre-tensioner drive from exerting a torque on said belt spool as a consequence of said activation of said belt tensioner drive.
 2. The method according to claim 1, characterized in that a flux of force from said pre-tensioenr drive to said belt spool is interrupted as a consequence of said activation of said belt tensioner drive.
 3. The method according to claim 1, characterized in that the belt tensioner drive has a pyrotechnic gas generator which is actuated when said belt tensioner drive is actuated and which prevents said pre-tensioner drive from exerting a torque on said belt spool.
 4. The method according to claim 3, characterized in that activation of said pyrotechnic gas generator displaces a separating element from an initial position, in which said pre-tensioner drive is drivingly connected to said belt spool in a direction for winding said safety belt onto the belt spool and hence for pre-tensioning said safety belt, into a separating position in which said pre-tensioner drive is disconnected from said belt spool.
 5. The method according to claim 3, characterized in that activation of said pyrotechnic gas generator displaces a connecting element from an initial position, in which said pre-tensioner drive is drivingly connected to said belt spool in a direction for winding said safety belt onto said belt spool and hence for pre-tensioning said safety belt, into a separating position in which said pre-tensioner drive is disconnected from said belt spool.
 6. The method according to claim 1, characterized in that said pre-tensioner drive has an electric motor and in that activation of said belt tensioner drive interrupts a current supply of said electric motor.
 7. The method according to claim 1, characterized in that said pre-tensioner drive has an electric motor and in that activation of said belt-tensioner drive results in operation of said electric motor in a direction for unwinding said safety belt.
 8. The method according to claim 1, characterized in that both said pre-tensioner drive and also said belt-tensioner drive are uncoupled from said belt spool by a rotation of said belt spool in an unwinding direction of said safety belt.
 9. A belt retractor for a safety belt, having a belt spool, a pre-tensioner drive with a drive motor which can rotate said belt spool in a winding direction so as to pre-tension a safety belt, and having a belt tensioner drive which can drive said belt spool so as to tension a safety belt, characterized in that a safety mechanism is provided which through an activation of said belt tensioner drive prevents said pre-tensioner drive from driving said belt spool in said winding direction.
 10. The belt retractor according to claim 9, characterized in that said safety mechanism has a separating element.
 11. The belt retractor according to claim 10, characterized in that said separating element is adapted for mechanically separating a connection from said pre-tensioner drive to said belt spool.
 12. The belt retractor according to claim 11, characterized in that said separating element separates a shaft.
 13. The belt retractor according to claim 11, characterized in that said pre-tensioner drive has one f a belt drive and a chain drive and that said separating element is adapted to destroy said belt or said chain.
 14. The belt retractor according to claim 11, characterized in that said pre-tensioner drive has a planetary gear and that said separating element can destroy a support which is fixed to said housing.
 15. The belt retractor according to claim 11, characterized in that said pre-tensioner drive has a toothed wheel gear and that said separating element can make a bearing of said gear inoperative.
 16. The belt retractor according to claim 11, characterized in that said pre-tensioner drive has a toothed wheel gear and that said separating element can transfer a connecting pin from an initial position, in which it can transfer a torque from one component of said gear to another, into a separating position.
 17. The belt retractor according to claim 11, characterized in that said pre-tensioner drive has a coupling and that said separating element brings said coupling into an uncoupled state or holds it in said uncoupled state.
 18. The belt retractor according to claim 9, characterized in that said separating element interrupts a supply of a drive motor.
 19. The belt retractor according to claim 18, characterized in that said separating element is a switch.
 20. The belt retractor according to claim 18, characterized in that said separating element destroys at least one supply line for said drive motor.
 21. The belt retractor according to claim 18, characterized in that said separating element is part of a buckle- or end fitting tensioner.
 22. The belt retractor according to claim 18, characterized in that said separating element short-circuits supply lines of said drive motor.
 23. The belt retractor according to claim 1 (, characterized in that said separating element reverses a direction of rotation of said drive motor.
 24. The belt retractor according to claim 9, characterized in that said belt tensioner drive has a pyrotechnic gas generator and that said separating element is driven by a gas pressure which is generated upon activation of said belt tensioner drive. 